The use of an intra-oral scanner for patellar surface analysis in total knee arthroplasty

Using an intra-oral scanner for surface and contact evaluation is a novelty in orthopaedics. We introduced this method to compare the congruence between patellar and femoral component surfaces. The compared patellar surfaces were created either with resurfacing, retention of an un-resurfaced patella or patelloplasty, a reshaping method where both facets are resected to match the trochlear surface. In our prospective clinical study, two patients had their patellar surfaces scanned during knee endoprosthesis (Genesis II, Smith & Nephew) implantation, using TRIOS® (3Shape) intraoral laser scanner. Each patient’s patella was scanned three times. First, the original joint surface was scanned after arthrotomy, then scanned again after reshaping the patellar surface and finally scanned after resurfacing with the appropriate standard implant was performed. The acquired surface data were evaluated using CloudCompare software. A mathematical algorithm was used to achieve the best proximity between these surfaces. Distances between the surfaces were measured throughout 0–120° of knee flexion. We defined the measure of proximity as "contact area magnitude". On average, the contact area magnitude was 2.91±0.82 mm using the un-resurfacing method, 3.19±0.95 mm using the resurfaced method and 3.84±0.91 mm using patelloplasty. Leaving the patella un-resurfaced resulted in an improved contact area magnitude. The proximity of the surfaces increased with knee flexion until 75°. With this study, the use of an intra-oral scanner for the surface analysis and intraoperative congruence evaluation was demonstrated. This method could contribute to a better understanding of patellofemoral congruence during total knee arthroplasty.